Only 1 Collapsing Header Open At A Time

Is there any way currently to implement multiple collapsing headers, only one of which can be open (when another is clicked, the previous will close)? I've tried fiddling around with calling the `open` functions of other collapsing headers from within a collapsing header but I can't get anything to work correctly.
If not, then it would be great if this were added.

No files or tests are named. Start by locating egui's collapsing-header API and the open functions mentioned in the issue, then inspect how multiple headers are typically composed. Done means opening one header reliably closes any other header in the group, with the behavior covered by an appropriate test or example.

Written by the indexing model from the issue text.